The Se concentration of seven Florida Land Pebble deposit phosphate rocks ranged from 0.7–7.0 ppm. The range was 1.4–178 ppm Se in seven samples from the western phosphate field. The Meade Peak phosphatic shale member of the Phosphoria formation contains more Se than rock from other phosphatic formations. Normal and concentrated superphosphates made from phosphatic rocks containing 100 ppm Se can be expected to contain about 60 and 40 ppm Se, respectively. Laboratory‐prepared concentrated superphosphate containing 23 ppm Se applied to an alkaline soil that normally produced alfalfa (Medicago sativa L.) low in Se at a rate of 156 ppm P increased Se concentration in alfalfa above the minimal requirements to protect livestock from white muscle disease. Concentrated superphosphate and single superphosphate prepared from phosphate rock containing 178 ppm Se and applied at a rate of 80 ppm P increased the Se concentration in alfalfa compared to the same amount of P applied as Se free concentrated superphosphate. Normal phosphate fertilizer practices can provide required Se for livestock provided the fertilizer is prepared from phosphate rock containing sufficient Se.

Two laboratory-prepared ferric hydroxy bi-selenites and CuSeOs applied to Portneuf silt ham in the field provided slowly available Se to alfalfa, resulting in Se concentration adequate but nontoxic for livestock. These materials have potential as Se fertilizers at low application rates. The ferric hydroxy bi-selenites offer little or no advantage over CuSe0s. Se from BaSe04 alone, BaSeO4-BaSO4 mixtures, and CuSe04 was absorbed by alfalfa in concentrations toxic to livestock A small fraction of applied elemental Se was available immediately after application, providing adequate Se to alfalfa for livestock. The remaining elemental Se was rather inert, and supplies only slightly more Se to alfalfa than did the untreated soil the year following application.